Question

我有一个运行良好的程序，但即使我在main.m中有一个NSLog文件，我也没有打印输出你能告诉我什么是错的吗？谢谢。

的main.m

#import <Foundation/Foundation.h>
#import "Stockholding.h"

int main(int argc, const char * argv[])
{

  @autoreleasepool {

    StockHolding *stockA;
    StockHolding *stockB;
    StockHolding *stockC;

    [stockA setPurchaseSharePrice:2.40];
    [stockA setCurrentSharePrice:3.12];
    [stockA setNumberOfShares:40];

    [stockB setPurchaseSharePrice:1.50];
    [stockB setCurrentSharePrice:1.41];
    [stockC setNumberOfShares:35];

    [stockC setPurchaseSharePrice:1.10];
    [stockC setCurrentSharePrice:1.20];
    [stockC setNumberOfShares:60];


    NSArray *holdings = [NSArray arrayWithObjects:stockA, stockB, stockC, nil];

    for (StockHolding *n in holdings) {
      // Call the methods
      float cost = [n costInDollars];
      float value = [n valueInDollars];
      NSLog(@"Bought stock for $%.2f, It is now at $%.2f, I have %d shares, They cost me $%.2f, Now they are worth $%.2f", [n purchaseSharePrice], [n currentSharePrice], [n numberOfShares], cost, value);
    }
  }
    return 0;
}

StockHolding.h

#import <Foundation/Foundation.h>

@interface StockHolding : NSObject {
  float purchaseSharePrice;
  float currentSharePrice;
  int numberOfShares;
}

@property float purchaseSharePrice;
@property float currentSharePrice;
@property int numberOfShares;

-(float)costInDollars;
-(float)valueInDollars;

@end

StockHolding.m

#import "StockHolding.h"

@implementation StockHolding

@synthesize purchaseSharePrice, currentSharePrice, numberOfShares;

-(float)costInDollars
{
  return (purchaseSharePrice * numberOfShares);
}

-(float)valueInDollars
{
  return (currentSharePrice * numberOfShares);
}

@end

Answer 1

您实际上并未创建任何StockHolding个对象。因此，您的数组为空，循环不执行任何操作。

StockHolding *stockA;

只是指针的声明。您需要创建它指向的对象;通常的程序是：

StockHolding *stockA = [[StockHolding alloc] init];

因为在ARC下，对象指针被初始化为nil（意思是“没有对象”），所以你将nil作为所有参数传递给arrayWithObjects:。 nil是哨兵值意味着“没有更多参数”，数组是在没有内容的情况下创建的。

对于空数组，for (StockHolding *n in holdings)没有任何可以枚举的内容，因此循环体中的所有代码（包括NSLog()）都不会被执行。

Xcode中没有打印输出

1 个答案: